Abstract: Over the past decades, the expansion of natural secondary forests has played a crucial role in offsetting the loss of primary forests and combating climate change. Despite this, there is a gap in our understanding of how tree species' growth and mortality patterns vary with elevation in these secondary forests. In this study, we analyzed data from two censuses (spanning a five-year interval) conducted in both evergreen broadleaved forests (EBF) and temperate coniferous forests (TCF), which have been recovering for half a century, across elevation gradients in a subtropical mountain region, Mount Wuyi, China. The results indicated that the relative growth rate (RGR) of EBF (0.028 ± 0.001 cm·cm⁻¹·a⁻¹) and the mortality rate (MR) (20.03% ± 1.70%) were 27.3% and 16.4% higher, respectively, than those of TCF. Interestingly, the trade-off between RGR and MR in EBF weakened as elevation increased, a trend not observed in TCF. Conversely, TCF consistently showed a stronger trade-off between RGR and MR compared to EBF. Generalized linear mixed models revealed that elevation influences RGR both directly and indirectly through its interactions with slope, crown competition index (CCI), and tree canopy height (CH). However, tree mortality did not show a significant correlation with elevation. Additionally, DBH significantly influenced both tree growth and mortality, whereas and CH and CCI had opposite effects on tree growth between EBF and TCF. Our study underscores the importance of elevation in shaping the population dynamics and the biomass carbon sink balance of mountain forests. These insights enhance our understanding of tree species' life strategies, enabling more accurate predictions of forest dynamics and their response to environmental changes.

Key words: Trade-offs, Generalized linear mixed models (GLMM), Remote sensing, Secondary forest, Mount Wuyi